Rolling cutter mounting in big hole reaming bit

ABSTRACT

A reaming type rock boring drill having an innermost cutter, rotatably supported as a beam. A sleeve or other support member disposed close to, but spaced apart from, the drill stem that forms a portion of the bit body serves as a trunnion or journal for the inner end of the load pin of the cutter bearing assembly. Drilling with such an assembly results in an uncontacted kerf of rock contiguous with the pilot hole. This kerf is disintegrated by mounting the innermost cutter so that the forces applied to the borehole bottom by this cutter act along a line directed into the formation and inwardly toward the pilot hole. As a result, a much higher cutting efficiency is achieved, when contrasted with earlier dispositions in which the innermost cutter acted directly on the bottom of the bore hole immediately adjacent the pilot hole.

United States Patent Pessier Aug. 7, 1973 Primary ExaminerMarvin A. Champion Assistant Examiner-Jack E. Ebel Attorney-R. A. Fel'sman [57] ABSTRACT A reaming type rock boring drill having an innermost cutter, rotatably supported as a beam. A sleeve or other support member disposed close to, but spaced apart from, the drill stem that forms a portion of the bit body serves as a trunnion or journal for the inner end of the load pin of the cutter bearing assembly. Drilling with such an assembly results in an uncontacted kerf of rock contiguous with the pilot hole. This kerf is disintegrated by mounting the innermost cutter so that the forces applied to the borehole bottom by this cutter act along a line directed into the formation and inwardly toward the pilot hole. As a result, a much higher cutting efficiency is achieved, when contrasted with earlier dispositions in which the innermost cutter acted directly on the bottom of the bore hole immediately adjacent the pilot hole.

5 Claims, 4 Drawing Figures Pmmwm 11w 3.750.767

SHIT 1 UF 2 RUDOLF CARL OTTO PESSIER I N VEN TOR.

ATTORNEY mean-10m 1m SHEU 2 9? 2 RUDOLF CARL OTTO PESSIER ATTORNEY ROLLING CUTTER MOUNTING IN BIG HOLE 'REAMING BIT BACKGROUND OF THE INVENTION l.Field of the Invention This invention relates generally to large diameter rock boring drills employing rolling cutters to disintegrate the bottom of a borehole formed in rock formations. More particularly, it concerns the mounting of such rolling cutters on a bit body, saddle-mounted rolling cutters having now become the standard of the industry. Even more particularly, the present invention deals with those innermost rolling cutters mounted to disintegrate the bore hole bottom adjacent a pilot hole.

\ Since the bit is designed to enlarge a pilot hole, it may be more accurately classified as a reaming bit rather than a full hole bit.

Further with respectto classification, abig hole bit, whether designed to drill a full hole in one pass orto enlarge 21 previously drilled :pilot hole, may be distinguished from smaller bits by the amount of space available for mounting the rolling cutters. When the hole is so small that it isnot possibleor reasonable to saddlemount the cutters, thebit could be classified as a small hole bit. Conversely, where the hole to be drilled is largeenoughto saddlemount all cutters, as in the present lnventiomthe bit maybe classifiedas a big holebit.

2. Description of thePrior Art The designing of a big hole reamer is complicated by ,thefactthat virtually all of the pilot hole is occupied by a sectionof drillstem which is tightly secured tothe bit body. The mounting of the innermost rolling cutter or cutters has been particularly vexatious, since it has been seemingly advantageous that such cutters be "mounted to cut'all the way up to the'borewallof the "pilot hole. Todo'this and yet mount the innermost cutters for support at each endhas required using the drill stem as the inner support member for the innermost cutters, Breaching the drill stem isundesirablebecause it is already highly stressed asthe result of the pulling and turning forces exerted on it. Any opening in it, such as theprior artopening to form aninner support for the central most rolling cutters, creates a weak spot where failure is likely to occur.

SUMMARY OF THE INVENTION It is therefore theprincipal objec't'ofthe present invention to p'rovidea mounting'structure for the innermost rolling cuttersofa big hole reaming bit which does not require the direct use of the drill stem of the bit tosupport the inner end of the cutter.

Stated "another waygit is an object of the present invention to saddle mount theinnermost cutters of a big "hole reaming bitbysupplying for. the two support members structure otherthan the drill stem of the bit.

The above and other objects are achieved according to the present invention by first of all ,providing an inner supportmember which may take the form of a sleeve surrounding a portion of the drill ,stempassing through the center of the array of cutter assemblies mounted on the bit'body. This sleeve is firmly secured to the face plate of the bit body, butpreferably is not secured to the drill stem itself. The saddle for each of the innermost cutters is modified, by comparison with those used for intermediate rolling cutter supports and the supports for the gage cutters, so that it furnishes only the outer journal support for the innermost cutter, the inner support being furnished by the sleeve. The support furnished by the sleeve member may take variousforms, forinstance a simple hole through the sleeve which receivesthe load pin about which the cutter rotates. The sleeve and saddle are disposed to mount an innermost cutter so that its lowermost cutting edge comes into contact with the borehole bottom along a line defining an acute angle with the unreamed pilot hole. Expressed another way, a conical innermost cutter is disposedwith the large base of the cone at a larger radial distance from the bit axis than the small base, and so that the large base leads the small base into the bottom of thehole.

When thrust is applied against the formation through a cutter so disposed, it will be exerted both in the axial direction in which'the bit is advancingand inwardly to ward the axis of the bit,the resultant force having a line of action slanted inwardly-forwardly with respect to suchaxis. This insures a force against the portion of the uncut rock immediately adjacent the pilothole, and causes such rock to fracture and slough off in the form of relativelylarge pieces.

The above and other objects, featuresand advantages of the invention will become more fully apparent with reference to the following description.

BRIEFDESCRIPTION OF THE DRAWING FIG. 1 isa perspective. view of a complete big hole rolling cutter bit utilizing the innermost cutting assemblies of the :present invention. The particular bit illustratedis a-inch mine raise drill bit shown in position for upward reaming of a pilot hole.

FIG. 1A is a perspective view of only portions of the big hole bit of FIG. 1, specificallyone of the innermost cutter assemblies, the sleeve which fumishesthe inner journal for suchcutter assembly, partially broken away to show the nature of the bearing, and the shim only of another innermost cutter'assembly.

FIG. 2is a plan view of the complete innermost cutter assembly .of FIG. 1A, together withthe cooperating half of the supporting sleeve and the drill stern inside the sleeve,.parts being sectionedin the interest of clarity;

FIG. 3 is an elevation of half of the complete big hole rolling cutter bit of FIG; 1, the view being taken to obtain a side view of one of the innermost cutter assemblies and show its action on the formation being drilled.

' DESCRIPTION OF THE PREFERRED EMBODIMENT The major partsof the complete bit consist ofa supporting body 2, a drill stein section or sub 4 passing through the center of the body and integrally secured thereto, and in this instance nine cutter assemblies welded or otherwise firmly secured to upper surface 26 of the bit body. The cutter assemblies are disposed in three annular rows of increasing radius, two inner cutter assemblies 6, three intermediate cutter assemblies 8 and four outer or gage cutter assemblies 10. As seen in FIGS. 1 and 3, the bit body 2 consists of the heavy face plate 16, a thinner and narrower base plate 18 spaced below face plate 16, a sleeve 22 or inner portion of an inner cutter assembly support means extending between the two plates, and a multiplicity of ribs 20 extending radially from sleeve 22 between the pair of plates. These members are all welded together to form a strong, unitary body or base. The drill stem 4 and sleeve 22 together extend from the bottom of plate 18, where these two preferably cylindrical members are secured by a circumferential weld 19. Sleeve 22 terminates at the bottom of face plate 16, while drill stem 4 extends onward through face plate I6 and sleeve 12 into the cluster of cutter assemblies. Drill stem 4 projects upwardly from sleeve I2 and above the bit as a whole to terminate in a tapered and threaded pin 14 for connection to another section of drill stem. The lower end of sleeve 12 is connected by suitable means, such as by welding, to the face plate 16.

In general, the mounting means used for intermediate cutter assemblies 8 and gage cutter assemblies exemplify the prior art mountings of the inner cutters. As shown in FIG. 1, each outer cutter assembly 10 consists of a saddle 36 having a base portion 37 welded to a shim 28 at 29, the shim being welded to face plate 16 at 30. Each outer assembly 10 also includes an inner arm 43 andan outer arm 45 forming a part of each saddle 36. A rolling cutter 47 is mounted between the saddle arms 43 and 45 on a load pin or other bearing member 49 which extends from both ends of the rolling cutter into coaxially aligned openings in the two saddle arms. The load pin 49 is typically a non-rotating member, and is typically secured to each saddle arm by a bolt 58 extending transversely through registering openings in the saddle arm and load pin 49. The shim 28 on which the saddle 36 rests and is secured may be thought of as a part of the face plate 16 to which it is welded. The slope of the shim is varied in accordance with the angle needed between the axis of rotation of the cutters and the axis 48 of the bit.

As best seen in FIG. 1A, the mounting saddle used with each inner cutter assembly 6 of the invention as part of the inner cutter'assembly support means has only a base portion 44 welded to shim 32 at 38 for supporting an outer saddle arm 40, the inner saddle arm having been removed at 42 so that itdoes not support the inwardly projecting portion-"of load pin 50. An appropriate radial opening 34 is formed in sleeve 12, and this opening receives the inwardly projecting end of load pin 50 in load bearing relationship. The arrangement avoids any need for the load pin to extend into the drill stem, but leaves a radial gap 51, such that the sleeve is flexably mounted to'the face plate 16 to permit lateral movement, of all except its welded lower end, relative to the drill stem section or sub 4. As seen in FIG. 2, the rearward end portion of the load pin 50 extends into an aperture 52 formed in saddle arm 40, and is retained by a fastener assembly 58,60 extending through aperture 54 in arm'40 and aperture 56 in load pin 50.

However, with cutter 46 disposed as shown in FIGS. 1A and 3 to exert force into the formation and inwardly toward the bit axis, the portions of the rock formation adjacent the pilot hole become highly stressed and weakened. As indicated in FIG. 3, a chip B of uncut rock breaks off just in advance of the bit, and similar chip C will become dislodged and break off shortly thereafter. Thus, there is little or no problem with respect to the kerf A which is untouched by a cutter, even though such kerf may have a radial thickness of 1% to 2% inches in the 60-inch reaming type bit illustrated.

In addition, applicant has discovered that cutters 46 when mounted as described wear evenly, the compacts (tungsten carbide drilling inserts) closest to center dulling at about the same rate as those which drill at larger radii by contrast with the accelerated wear of the same outer compacts in prior art mountings whereby the innermost cutters were supported by the drill stem and cut all the way up to the pilot hole.

While the invention has been shown in only one of its forms, it should be apparent to those skilled in the art that it is not thus limited, but is susceptible to various changes and modifications without departing from the spirit thereof.

I claim:

1. In a big hole reaming rock bit utilizing at least one rolling cutter supported on a bit body attached to a drill stem to cut that portion of a borehole bottom adjacent a pilot hole, the improvement comprising a sleeve secured to the bit body to surround with a circumferential radial gap the drill stem, which is rigidly secured to the bit body, and an innermost cutter assembly also secured to the bit body and supporting the outer end of a load pin about which said cutters rotate, said load pin also extending radially inwardly and being received and supported in an opening in said sleeve.

2. Support structure for an innermost rolling cutter of a big hole reaming rock bit having a base and a drill stem rigidly secured to the base and projecting upwardly therefrom, said structure comprising a pair of upwardly extending support members secured to said base and supporting opposed ends of said cutter, the supporting end region of one of said support members being adjacent, but spaced apart from said drill stem in the region that supports the inner end of the cutter to permit lateral movements independent of the drill stem, the other of said support members being radially spaced from the first to support the outer end of the cutter.

3. An improved inner mount for a saddle mounted rolling cutter load pin of a reaming big hole rock bit comprising a bit body, a rigid drill stem secured to and projecting from said body, a sleeve flexibly secured to said bit body forjndependent lateral movement and closely adjacent its drill stem, said sleeve having an opening therein to receive and support the inner end of said rolling cutter load pin, and a saddle mounted to said bit body to support the outer end of said rolling cutter load pin.

4. An improvement in bits used for reaming pilot holes, said bit comprising a rigid drill stem section, plate means extending transversely from said drill stem section, rolling cutter assemblies including inner and outer cutter assemblies secured to the plate means, an inner cutter assembly support means including an circumferentially extending innermost upwardly extending portion secured to said plate means in radially spaced relationship with said drill stem section, a load pin to support the roller cutter of said inner cutter assembly and having an inner end extending into the incutter assembly secured to the plate means, a sleeve secured to the plate means and having a portion defining a circumferential radial gap with the drill stem section, a load pin to support the rolling cutter of said inner cutter assembly, with an inner end extending into engagement with said sleeve for support and an outer end being supported by the inner cutter assembly. 

1. In a big hole reaming rock bit utilizing at least one rolling cutter supported on a bit body attached to a drill stem to cut that portion of a borehole bottom adjacent a pilot hole, the improvement comprising a sleeve secured to the bit body to surround with a circumferential radial gap the drill stem, which is rigidly secured to the bit body, and an innermost cutter assembly also secured to the bit body and supporting the outer end of a load pin about which said cutters rotate, said load pin also extending radially inwardly and being received and supported in an opening in said sleeve.
 2. Support structure for an innermost rolling cutter of a big hole reaming rock bit having a base and a drill stem rigidly secured to the base and projecting upwardly therefrom, said structure comprising a pair of upwardly extending support members secured to said base and supporting opposed ends of said cutter, the supporting end region of one of said support members being adjacent, but spaced apart from said drill stem in the region that supports the inner end of the cutter to permit lateral movements independent of the drill stem, the other of said support members being radially spaced from the first to support the outer end of the cutter.
 3. An improved inner mount for a saddle mounted rolling cutter load pin of a reaming big hole rock bit comprising a bit body, a rigid drill stem secured to and projecting from said body, a sleeve flexibly secured to said bit body for independent lateral movement and closely adjacent its drill stem, said sleeve having an opening therein to receive and support the inner end of said rolling cutter load pin, and a saddle mounted to said bit body to support the outer end of said rolling cutter load pin, and a saddle mounted to said bit body to support the outer end of said rolling cutter load pin.
 4. An improvement in bits used for reaming pilot holes, said bit comprising a rigid drill stem section, plate means extending transversely from said drill stem section, rolling cutter assemblies including inner and outer cutter assemblies secured to the plate means, an inner cutter assembly support means including an circumferentially extending innermost upwardly extending portion secured to said plate means in radially spaced relationship with said drill stem section, a load pin to support the roller cutter of said inner cutter assembly and having an inner end extending into the innermost upwardly extending portion of the inner cutter assembly support means and an outer end extending into an outermost upwardly extending portion of the inner cutter assembly support means.
 5. An improvement in bits used for reaming pilot holes, said bit comprising a rigid drill stem section, plate means extending transversely from said drill stem section, rolling cutter assemblies including an inner cutter assembly secured to the plate means, a sleeve secured to the plate means and having a portion defining a circumferential radial gap with the drill stem section, a load pin to support the rolling cutter of said inner cutter assembly, with an inner end extending into engagement with said sleeve for support and an outer end being supported by the inner cutter assembly. 